Vapor Permeation Cure (VPC) using vaporized basic materials such as tertiary amine catalysts are well documented in the prior art and described for example in U.S. Pat. Nos. 4,343,924; 4,365,039; 4,366,193 and references incorporated therein. This method of curing is preferred over prior baking procedures for certain heat sensitive substrates, particularly certain thermoplastics, photographic films and several coating compositions required to meet certain minimum performance specifications such as mar and deformation resistance and minimal discoloration. Vapor phase curing is effected within a shortened period of time, usually less than one minute, and at significantly reduced temperatures; thus minimizing substrate deformation. In practice however, these prior processes are found to have several drawbacks and unexpected impediments in their synthesis schemes, among which is the need for a resin dispersion solvent and other additives to achieve uniform coatings. Also, some amino vapor cure processes still require temperatures at which many substrates undergo some degree of deformation. For example, the Vapor Permeation Cure described in U.S. Pat. No. 2,967,117 on a coating of polyhydroxy polyester and polyisocyanate is cured at 80.degree.-120.degree. C. in the presence of gaseous tertiary amine or phosphine. The addition of fugitive solvents which are subsequently removed and other additives unnecessarily add to the cost and efficiency of such curing processes and, in some instances, diminish beneficial properties of the coating material by dilution of their effectiveness.
Accordingly, it is an object of the present invention to overcome the shortcomings and difficulties encountered in the above noted processes and to provide a hardened or fully cured, more concentrated coating having infinitely extended shelf-life which coating can be simultaneously applied and cured on a substrate within a few seconds of exposure at room temperature by a vapor phase process.
Another object of the invention is to provide a more efficient, more economical vapor hardening process for heat sensitive coatings or coated substrates.
These and other objects and advantages of the invention will become apparent to the skilled artisan from the following description and disclosure.